This is likely a fungus called blossom end rot. We would recommend using Bonide Rot Stop Tomato Blossom End Rot. helps to correct a disorder in plants caused by a lack of calcium. Blossom end rot is visible on the end of the fruit as a sunken brown spot opposite the stem. Use Bonide Rot-Stop Tomato Blossom End Rot to provide the nutritional calcium needed for developing fruit or after periods of heavy rain. This is a ready to use product and can be applied every 5-7 days as needed.
Answer last updated on: 07/01/2016